The invention relates in general to devices such as sewing machines for joining parts together and in particular to a new and useful procedure for feeding and positioning at least two workpiece sheets intended to be treated together or connected to each other.
In a procedure for aligning and leading together limp workpiece sheets known from U.S. Pat. No. 4,176,832 they are laid individually on a horizontal support. Subsequently, the current alignment position is determined by scanning at least a portion of their edges and with the aid of the values obtained an alignment process is carried out, in which the workpiece sheets are shifted on the support.
A condition for perfect alignment results is, however, that the workpiece sheets are in a state suitable for scanning, that is, the workpiece sheets have to be spread out planarly.
While small dimensioned and relatively stiff workpiece sheets assume a planar position on their own without special measures, in the case of large workpiece sheets which are, in addition thin and flexible, care must be taken to avoid folds or waves and, particularly turned under edges or eliminate them. Therefore, after placing the workpiece sheets they might possibly have to be smoothed out by hand. Because of the alignment principle based on which sensor driven pointlike holding elements acting upon the workpiece sheets force relative motion between the support and the workpiece sheets, there is the danger in aligning very flexible workpiece sheets that these might be warped by the resulting frictional force.
From the German OS 34 36 965 a process for aligning limp workpiece sheets is known in which the sheets are placed in a plane and without being warped on a support by specific conveyor devices. Special technological measures are employed in order to position the workpiece sheet in a way which would permit scanning, that is, spread out planarly for subsequent scanning and aligning. The bringing together of several workpiece sheets with respect to exact positions for subsequent common processing requires relatively high expenditures since for this purpose, a suction holder equipped conveying device is employed which must be precisely controlled.